State of the Art
The invention relates to a flowmeter for gases, the sensor of which has a housing which is open at two opposite ends for the infeed and discharge of the gases to be measured, and in which a rotor is rotatable about an axis between two stators which consist of deflection blades which are substantially at right angles to the axis, while optical means are arranged to detect the rotation of the rotor and convert it into an electrical output signal.
Such a flowmeter has been used by applicants, in particular in various instruments for measuring and analyzing breathing gases. The sensor has a housing which is circular cylindrical. The stators are formed by a metal disc in which are set a number of blades which are flat per se, and which all lie at an angle relative to axial faces. This slanting position is necessary to ensure that axially inflowing gases can be converted into a vortex which is capable of setting the rotor in rotation, the rotor being designed as a small vane which lies in an axial plane with an axis of rotation corresponding to the central axis of the sensor. As a result of the sudden deflection undergone by the inflowing gases, a flow pattern whose type depends to a large extent on the absolute value of the rate of flow of the gases, is produced.
It is possible to eliminate the consequences of this through calibration, but the problem then encountered is that the individual sensors doe not have any reproducible features. They are not even bidirectional. Each instrument thus has to be calibrated separately, and the sensor may be placed in only one specific position. It is thus not possible to compensate for the non-linearities in the features by means of a hardware or software, because it is necessarily identical for all instruments.
These problems are caused by the fact that for the known sensor there is no method of production other than by manual labor, whereby the blades are fixed individually relative to the little disc forming the center piece of each stator, while everything is moreover glued by hand in the cylindrical housing.